Abstract

We report the first entanglement swapping experiment using entangled photon-pair sources based on spontaneous four-wave mixing (SFWM). The 1.5-µm band entangled photon pairs generated by SFWM in two independent 500-m dispersion shifted fibers exhibited quantum interference, thanks to the negligible walk-off between the pump and photon pairs. The use of 500-MHz gated-mode InGaAs/InP avalanche photodiodes based on the sine-wave gating technique increased the fourfold coincidence rate. As a result, the formation of an entanglement between photons from independent sources was successfully observed.

(a) HOM measurement result. The vertical axis shows the fourfold coincidences obtained by the TIA for 1,000,000 start pulses. The detection signals from Alice’s and Bob’s detectors were used as the start and stop pulses for the TIA. Alice’s and Bob’s detectors were gated using the detection signal from the detectors owned by Charlie. (b) Two-photon interference fringe obtained using coincidence counts of two signal photons conditioned by Bell state measurement of idler photons. The vertical axis shows the coincidence rate per start pulse. Squares: TA=32.25°C, circles: TA=32.35°C. Statistical error bars are given only for the data with TA=32.25°C. Note that no accidental coincidences or noise counts have been subtracted from the data shown in (a) and (b).